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Calculate the Fiber-Optic Cable Power Budget

To ensure that fiber-optic connections have sufficient power for correct operation, calculate the link's power budget when planning fiber-optic cable layout and distances. This planning helps you ensure that fiber-optic connections have sufficient power for correct operation. The power budget is the maximum amount of power the link can transmit. When you calculate the power budget, you use a worst-case analysis to provide a margin of error. You use a worst-case analysis even though not all the parts of an actual system operate at the worst-case levels.

To calculate the worst-case estimate for a fiber-optic cable power budget (PB) for the link:

  1. Determine values for the link's minimum transmitter power (PT) and minimum receiver sensitivity (PR). In the following example, we measure both (PT) and (PR ) in decibels relative to one milliwatt (dBm).

    PT = – 15 dBm

    PR = – 28 dBm

    Note:

    See the specifications for your transmitter and receiver to find the minimum transmitter power and minimum receiver sensitivity.
  2. Calculate the power budget (PB) by subtracting (PR) from (PT):

    – 15 dBm – (–28 dBm) = 13 dBm